Base station apparatus, mobile station apparatus, transmission method and receiving method in a CDMA/TDD mobile communication system

ABSTRACT

A base station apparatus in a CDMA/TDD mobile communication system is provided. A signal is formed employing a frame configuration with a plurality of time slots and spreading processing utilizes a long spreading code for identifying a cell and a short spreading code for acquiring frame synchronization. The base station apparatus includes a first control channel former that forms a first control channel including a symbol that is spread by a first short spreading code. A second control channel former forms a second control channel including a symbol spread by a second short spreading code and positioned at a same timing as the symbol spread by the first short spreading code.

The present application is a continuation application of U.S. patentapplication Ser. No. 10/255,705, filed on Sep. 27, 2002, now U.S. Pat.No. 7,039,003 which is a continuation of U.S. patent application Ser.No. 09/199,195, filed on Nov. 25, 1998, now U.S. Pat. No. 6,522,625which claims the benefit of Japanese Patent Application No. JP 9-345820,filed on Dec. 1, 1997, the subject matter of each of which is expresslyincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio communication apparatus andradio communication method in a CDMA/TDD radio communication system inwhich multiple accesses are performed by a spread spectrum communicationwhere information is spread with a spreading code to transmit in aspread frequency band and communications in the same radio frequency areperformed alternately via a reverse link and a forward link in timedivision.

2. Description of the Related Art

Conventionally, as a radio communication system using a CDMA (CodeDivision Multiple Access) system, US Standard IS-95 is known. As aduplex system in IS-95, FDD (Frequency Division Duplex) is used. As theduplex system, TDD (Time Division Duplex) is also known. In the TDDsystem, transmissions and receptions are performed in the same frequencyband, called a Ping-Pong system, where communications in the same radiofrequency are performed alternately via a reverse link and a forwardlink in time division.

A multiple access system is a link connection system where a pluralityof stations perform communications concurrently in the same frequencyband. The CDMA technique is used to perform multiple connections byspread spectrum communications where an information signal is spreadwith a spreading code to transmit in a spread frequency band.

A direct sequence spread spectrum system is a system where aninformation signal is multiplied by a spreading code in the spreading.In a direct sequence CDMA, a plurality of communication links share thesame frequency, thereby resulting in a problem (near-far problem) thatit is necessary to acquire the same communication level at eachreception side, which should be solved to achieve a CDMA transmissionsystem.

The near-far problem is severer in receptions of a base station forreceiving radio waves concurrently from a plurality of mobile stationslocated at different distances from the base station. Therefore, it ismandatory at mobile station sides to perform a transmission powercontrol corresponding to a state of each transmission path.

FIG. 1 is a schematic diagram illustrating base stations and a mobilestation in the base stations controlled communication areas. FIG. 1illustrates a case where three base stations are present.

In FIG. 1, the communication area of base station 1 is cell 5, thecommunication area of base station 2 is cell 6, and the communicationarea of base station 3 is cell 7. The scales and forms of communicationareas vary depending on propagation environments.

Mobile station 4 acquires synchronization of spreading codes transmittedfrom base stations 1 to 3 when turned on. First, mobile station 4extracts signals of base stations 1 to 3 from signals including signalsof base stations 1 to 3, and starts the synchronization acquisition ofthe spreading codes.

The initial synchronization acquisition is explained with reference toFIG. 2. FIG. 2 is a timing diagram of each cell frame and a longspreading code. In IS-95, base stations 1 to 3 are synchronous to eachother and the same basic timing is applied in transmission frames ofeach of cells 5 to 7. As spreading codes, a short spreading code and along spreading code are multiplexed to be used. The short spreading codeis, for example, 64 chips, and the long spreading code is, for example,40,960 chips.

In a forward link, a sort of long spreading code is common and one inthe system. Each of cells 5 to 7 uses the sort of long spreading code byshifting a phase (differing a timing of a head of the code). Generally,the timings of basic frames k, k+1 and k+2 of cells 5 to 7 are notconformed to the timing of the long spreading code. Accordingly, eachcell is identified by the phase shift variation (difference).

The system includes some physical channels, where timings ofcommunication channel frames (communication frames) and timings ofcontrol channel frames (control frames) except SYNC channel frames(synchronism frames) are conformed to the basic frames k, k+1 and k+2.

Only the timings of SYNC channel frames (SYNC frames) k′, k′+1 and k′+2are not conformed to the basic frames k, k+1 and k+2 but conformed tothe timing of the long spreading code.

A sort of short spreading code used in the SYNC channel is common andone in the system. Mobile station 4 detects the correlation of areceived signal with a spreading code in which the long spreading codeand the short spreading code of the SYNC channel are multiplied. Thecorrelation detection is performed by varying the timing gradually untilthe correlation level exceeds the threshold value.

In the above manner, mobile station 4 detects the timing of the longspreading code from either of cells 5 to 7. Since the timings of SYNCchannel frames k′, k′+1 and k′+2 are conformed to the timing of the longspreading code, it is possible to demodulate and decode SYNC channelsignals according to the timing of the long spreading code.

The SYNC channel informs a difference of timings between basic frames k,k+1, k+2 and the long spreading code of the current cell (cell 5 in theconfiguration in FIG. 1) and a difference of timings between basicframes k, k+1, k+2 and the long spreading code of the neighboring cell(cell 6 or 7 in the configuration in FIG. 1). Accordingly, mobilestation 4 is capable of acquiring the timing of basic frames k, k+1 andk+2, thereby allows mobile station 4 to demodulate and decode differentcontrol channel signal.

Since the SYNC channel also informs the difference of timings betweenthe long spreading code of the neighboring cell and basic frames, mobilestation 4 is capable of demodulating and decoding different controlchannels signals of neighboring cell 6 or 7 and of comparing a receptionlevel of cell 5 which SYNC channel is already detected with a receptionlevel of neighboring cell 6 or 7. Then mobile station 4 selects acontrol channel of another cell with higher reception level to receive.

However, in the conventional initial synchronization method describedabove, when it is assumed that the long spreading code length is, forexample, 32,768 chips (26.667 [ms]), it is necessary to repeat thecorrelation detection with respect to 32,768 timings (more than ifoversampling is considered). In this case, it takes 6.82 [s], as shownbelow, to repeat detecting the correlation in short spreading codelength (for example, 256 chips) 32,678 times (1/1.2288[MHz])×(256/2)×32768=6.82 [s]. In the case of calculating an average, ittakes a half of the time, which is 3˜4 [s]. Actually, the processingtime including call connection processing is regulated maximum 15 [s],which suggests that it takes relatively a long time to detect thecorrelation of the long spreading code.

In addition, the transmission power of the SYNC channel is a half thatof the communication channel. When it is assumed that the number ofconcurrently connected communication channels in a cell is, for example20, one-fortieth of the frequency utilization efficiency is decreased.Accordingly, the frequency utilization efficiency is decreased due tothe SYNC channel.

In FDD, frequency bands between a reverse link and a forward link aredifferent and communications in each link are continuously performed. Onthe contrary, in TDD, communications in the same frequency band arealternately performed in a reverse link and a forward link. In otherwords, in the case of receiving forward link signals in mobile stations,an area where a signal to be received is present and an area where asignal to be received is not present are switched. Before a mobilestation acquires the synchronization with a base station, a switchingtiming of the reverse link and the forward link is unknown to the mobilestation. In other words, in TDD, a mobile station has not acquired theswitching timing of the reverse and forward link.

Further, in the case where the switching timing of the reverse link andforward link is synchronized with the frame timing, the timings of thelong spreading code are limited by some of switching timings of thereverse and forward link in the frames. In other words, in TDD, in thecase of synchronizing the switching timing of the reverse and forwardlink with the frame timing, the long spreading code timings are limited.Such limitation brings a difficult planning of base station locations.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a radio communicationapparatus and a radio communication method in a CDMA/TDD radiocommunication system, that are capable of reducing a synchronizationacquisition time of a long spreading code without reducing a frequencyutilization efficiency and of facilitating an easy planning of basestation locations.

This object is achieved by detecting the correlation with only a shortspreading code common in the system to detect symbols with the highcorrelation value, where the detected symbols are spread with only theshort spreading code and provided in relation with a period of the longspreading code, and by detecting another short spreading code indicativeof the switching timing of reverse and forward link, which ismultiplexed in the same position in the detected symbols, so as toacquire the synchronization of the long spreading code and thesynchronization of the forward and reverse link switching, and thesynchronization of transmission frames.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating base stations and a mobilestation in base station controlled communication areas;

FIG. 2 is a timing diagram of each cell frame and a long spreading codein a conventional initial synchronization method in a CDMA/TDD radiocommunication system;

FIG. 3 is a diagram illustrating a symbol configuration for slots ofcontrol channels to explain an initial synchronization method in theCDMA/TDD radio communication system according to the first embodiment ofthe present invention;

FIG. 4 is a timing diagram for frames and slots of each cell and a longspreading code in an initial synchronization method in the firstembodiment;

FIG. 5 is a diagram illustrating a symbol configuration for slots ofcontrol channel 1 in the initial synchronization method in the firstembodiment;

FIG. 6 is a diagram illustrating a symbol configuration for slots ofcontrol channel 2 in the initial synchronization method in the firstembodiment;

FIG. 7 is a diagram illustrating a symbol configuration for slots ofcontrol channel to explain an initial synchronization method in theCDMA/TDD radio communication system according to the second embodimentof the present invention;

FIG. 8 is a diagram illustrating an another symbol configuration forslots of control channel to explain an initial synchronization of thesecond embodiment;

FIG. 9A is a diagram illustrating a pattern configuration in the casewhere a slot that is one-eighth of one frame is assigned to a forwardlink in a phase pattern of pilot symbols of control channel to explainan initial synchronization in the CDMA/TDD communication systemaccording to the third embodiment of the present invention;

FIG. 9B is a diagram illustrating a pattern configuration in the casewhere a slot that is one-sixteenth of one frame is assigned to a forwardlink;

FIG. 9C is a diagram illustrating a pattern configuration in the casewhere a slot that is one-thirty second of one frame is assigned to aforward link;

FIG. 10A is a diagram illustrating another symbol configuration forslots of control channel to explain an initial synchronization method inthe CDMA/TDD radio communication system according to the secondembodiment of the present invention;

FIG. 10B is a diagram illustrating a table in which code patterns and ahead of a long spreading code are described;

FIG. 11 is a block diagram of an initial synchronization section of atransmission and reception apparatus in the CDMA/TDD radio communicationsystem according to the fifth embodiment of the present invention; and

FIG. 12 is a block diagram of an initial synchronization section in atransmission and reception apparatus in the CDMA/TDD radio communicationsystem according to the sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The explanation below describes about the embodiments of a radiocommunication apparatus and a radio communication method in a CDMA/TDDradio communication system of the present invention with reference toattached drawings.

First Embodiment

FIG. 3 illustrates a symbol configuration diagram for slots of controlchannel to explain an initial synchronization method in a CDMA/TDD radiocommunication system according to the first embodiment of the presentinvention. In addition, a configuration of the CDMA/TDD radiocommunication system is explained with reference to FIG. 1 where theconventional configuration is explained.

That is, in FIG. 1, the communication area of base station 1 is cell 5,the communication area of base station 2 is cell 6, and thecommunication area of base station 3 is cell 7. The scales and forms ofcommunication areas vary depending on propagation environments.

Mobile station 4 acquires synchronization of spreading codes transmittedfrom base stations 1 to 3 when turned on. First, mobile station 4extracts signals of base stations 1 to 3 from signals including signalsof base stations 1 to 3, and starts the synchronization acquisition ofspreading codes.

The initial synchronization acquisition is explained with reference toFIG. 4. FIG. 4 is a timing diagram of each cell frame and a longspreading code.

In FIG. 4, a basic frame k is divided to eight slots that are Slots 0 to7. Due to TDD, forward links and reverse links are repeated alternately.It is assumed that even number slots (Slot 0, Slot 2, Slot 4 and Slot 6)are forward links and odd number slots (Slot 1, Slot 3, Slot 5 and Slot7) are reverse links.

Base stations 901 to 903 are synchronous to each other and cells 905 to910 have the same timings of transmission frame. Accordingly, thetimings of slots, i.e., Slots 0 to Slots 7 (switching timing of reverselink and forward link) are conformed in any cell of cells 5 to 7.

A short spreading code and a long spreading code are multiplied to useas a spreading code. In the forward link, one sort of the long spreadingcode is used commonly in the system. Each of cells 5 to 7 uses the sortof the long spreading code by shifting a phase (differing a timing of ahead of the code). Accordingly, each of cells 5 to 7 are identified bythe phase shift variation. Generally, the timings of basic frames k−1, kand k+1 of cells 5 to 7 are not conformed to the timing of the longspreading code.

In an example of channel configuration of the forward link in FIG. 3,the number of control channels (control ch) is four and the number ofcommunication channel (communication ch) is six. In addition, since aguard time is provided, a signal length of each channel is a littleshorter than a slot length in each Slot 0 to Slot 7. The guard time isprovided to prevent forward link signals and reverse link signals frombeing overlapped by delayed versions. In addition, in symbols indicatingcontrol channels and communication channels, which are indicated byrectangles, white part 101 represents an interval in which signals arenot transmitted, whole oblique line part 102 represents symbols that arespread with only the short spreading code, and half oblique line part103 represents symbols that are spread with the code in which the shortspreading code and the long spreading code are multiplied.

In communication channel signal, all of symbols are spread with the codein which the short spreading code and the long spreading code aremultiplied. In control channel signal 1, some of symbols are spread withonly the short spreading code, and the rest of symbols are spread withthe code in which the short spreading code and the long spreading codeare multiplied. In control channel signal 2, a symbol in each slot isspread with only the short spreading code, and at the rest interval inthe slot, symbols are not transmitted. The long spreading code iscommon, and the short spreading codes are different between eachchannel.

FIG. 3 illustrates an example in which the head of the long spreadingcode is shifted to the middle of Slot 2, which is assumed to be jthsymbol at time t1. In control channel signal 1, a symbol just before thehead of the long spreading code (j-1th symbol) in Slot 2 is spread withonly the short spreading code. Further, j-1th symbols in Slot 0, Slot 4and Slot 6 of control channel signal 1 are also spread with only theshort spreading code.

FIG. 5 is a diagram illustrating a configuration of symbols in the slotof control channel signal 1 illustrated in FIG. 3. This case illustratesan example where one slot is composed of 20 symbols. 4 symbols of 301from the first symbol to the fourth symbol are pilot symbols PL. In 15symbols from the fifth symbol to the nineteenth symbol, except the kthsymbol (in this case, k=9) 303, 14 symbols of symbols 302 from the fifthsymbol to the eighth symbol and symbols 304 from the tenth symbol to thenineteenth symbol are information symbols INFO. The twentieth symbol 305is the guard time where a signal is not transmitted.

PL301, INFO302 and INFO304 are spread with the code in which the shortspreading code and the long spreading code are multiplied. Symbol 303 isspread with only the short spreading code. The short spreading code usedin control channel signal 1 is a predetermined common code in thesystem. The common short spreading code is referred to as SC0.

The phase shift variation of the long spreading code is set so that thehead of the long spreading code is synchronized with one of 15 symbolsfrom the sixth symbol to twentieth symbol, while not synchronized withpilot symbols (from the first symbol to the fourth symbol) and a symboljust after the pilot symbol (the fifth symbol), in one slot amongforward link slots (Slot 0, Slot 2, Slot 4 and Slot 6). In this case,the number of the phase shift variations is 60.

FIG. 6 is a diagram illustrating a configuration of symbols in a slot ofcontrol channel signal 2 illustrated in FIG. 3. FIG. 6 illustrates anexample where one slot is composed of 20 symbols in the same manner asFIG. 5. In 19 symbols from the first symbol to the nineteenth symbol, 18symbols of symbols 401 from the first symbol to the eighth symbol andsymbols 403 from the tenth symbol to the nineteenth symbol are NULLsymbols, except for kth symbol (in this case, k=9). The twentieth symbol404 is the guard time GT.

In NULL401, NULL403 and GT404, signals are not transmitted. Symbol 402is spread with only the short spreading code. As a value of k, 15integer numbers from 5 to 19 are available. Accordingly, as the shortspreading code used in control channel 2, 15 sorts of the code areprepared. It is assumed that these 15 shorts of spreading codes are SC1to SC 15. According to the value of k, SCk-4 is selected from 15 sortsof the codes to use. For example, in FIG. 6 SC5 is used because of k=9.

Mobile station 4 does not acquire synchronization with base stations 1to 3 when turned on. Accordingly, mobile station 4 has not obtained thetiming of long spreading code, the slot timing (switching timing ofreverse link and forward link), and the frame timing. The followingprocessing is performed to detect the timing of long spreading code, theslot timing, and the frame timing.

As the first step, control channel signal are despread with the shortspreading code SC0. In this case, symbols with high correlation valueappear each 40 symbols (each 2 slots). Accordingly, it is suggested thatcandidates of the head of the long spreading code are symbols just afterthe 4 symbols with the high correlation value appearing in one framelength (160 symbols).

Next, as the second step, the symbols having the high correlation valuewith short spreading code SC0 are despread with each of the shortspreading codes SC1 to SC15. In this despreading processing, correlationvalue with one code is detected high. According to the number (SC1 toSC15) of code with the high correlation value, the value of k (5 to 9)is determined. In this manner, it is decided the symbol spread with theshort spreading code is the kth symbol in the slot. In other words, theswitching timing of forward link and reverse link is decided. Thereby,it is possible to despread the symbol other than the symbol despreadwith the short code only.

Next, as the second step, as the third step, each candidate symbol forthe head position of the long spreading code is despread in the forwardlink interval with the code in which the short spreading code and thelong spreading code are multiplied. In this manner, it is decided thatwhich one of four candidates is the head of the long spreading code.

Finally, as the fourth step, the short spreading code is multiplied bythe long spreading code LC at the timing of the long spreading LCaccording to exclusive-OR to obtain the multiplied code, with which thedespreading processing is performed to received signals. Candidates ofthe head of the long spreading code are decoded to judge the frametiming.

According to the above processing, mobile station 4 obtains the timingof the long spreading code, the switching timing, and frame timing ofreverse and forward link. That is, only four candidates are enough atthe first step to obtain the timing of the long spreading code, therebyallowing largely reducing of the synchronization acquisition time forthe long spreading code.

In addition, since two symbols in control channel signal 1 and controlchannel signal 2 of one slot are used in the synchronization acquisitionfor the timing of the long spreading code and the slot timing, the ratioof decreasing of the utilization efficiency for the synchronizationacquisition is reduced to 1/10 as compared to the case where all of 20symbols are used in the SYNC channel for the frame synchronization.

In addition, according to the second step, the switching timing ofreverse and forward link is obtained. Further, since control channelsignal 2 is provided, 15 symbols from the sixth symbol to the twentiethsymbol in a slot are available as a head of the long spreading code.

As described above, according to the first embodiment, in the CDMA/TDDradio communication system in which the short spreading code and thelong spreading code are multiplied to use, symbols spread with only theshort spreading code are provided at a certain interval, and the symbolsspread with only the short spreading code are detected. By thisprocessing, the acquisitions of synchronization for the long spreadingcode and the synchronization of switching reverse and forward link areperformed, thereby allowing reducing of the synchronization acquisitiontime.

In addition, the above embodiment describes about the case where thenumber of symbols spread with only the short spreading code each slot isone, however it may be provided a plurality of symbols spread with onlythe short spreading code each slot.

Further, the above embodiment describes about the case where the symbolspread with only the short spreading code is a symbol just before thehead of the long spreading code, however it is not necessary to alwaysprepare the symbol just before the head of the long spreading code whenthe symbol spread with only the short spreading code is related with thetiming of the long spreading code in advance.

In addition, the above embodiment describes about the case where nosignals are transmitted other than the kth symbol in control channelsignal 2, however it is preferable that other symbol information istransmitted in the same manner as control channel signal 1.

Second Embodiment

FIG. 7 is a diagram illustrating a symbol configuration for slots ofcontrol channels to explain an initial synchronization method in theCDMA/TDD radio communication system according to the second embodimentof the present invention. In addition, sections in the second embodimentillustrated in FIG. 7 corresponding to the sections in the firstembodiment illustrated in FIG. 3 are assigned the same symbols as thefirst embodiment to omit the explanation.

According to the initial synchronization method described in the firstembodiment, mobile station 4 acquires the synchronization for the longspreading code and the synchronization for the switching timing ofreverse and forward link. However, at this time, mobile station 4 hasnot recognized the slot number and has not acquired the transmissionframe synchronization.

The second embodiment describes about a method to further acquire thetransmission frame synchronization by presence and absence of symbolsspread with only the short spreading code and a phase in an in-phasecomponent-quadrature component plane.

The first description is about the method to acquire the transmissionframe synchronization by presence and absence of symbols spread withonly the short spreading code. FIG. 7 is a diagram illustrating a frameconfiguration of control channel signal 1 and control channel signal 2.The symbol configuration of slots in control channel signal 1 is thesame as that explained in the first embodiment illustrated in FIG. 5. Incontrol channel signal 2, no signals are transmitted in Slot 0 asillustrated in FIG. 7.

Mobile station 4 acquires the synchronization for the long spreadingcode and the synchronization for the switching timing of reverse andforward link according to the initial synchronization method explainedin the first embodiment, then searches the slot in which no signals aretransmitted in control channel signal 2.

The correlation values with each spreading code SCm(m=1 to 15) that isused in control channel signal 2 are detected, and the slot having nothigh correlation value is detected to decide Slot 0. The head of thedetected slot is thus recognized as the head of the transmission framebecause Slot 1 is placed at the head of the slot.

The next description is about the method to acquire the transmissionframe synchronization by a phase in the in-phase component-quadraturecomponent plane. FIG. 8 is a diagram illustrating another example offrame configurations of control channel signal 1 and control channelsignal 2.

Herein, it is assumed that the modulation system is QPSK (QuadraturePhase Shift Keying). As a phase of each symbol in the in-phasecomponet-quadrature component plane (IQ plane), 4 types of “00, 01, 10and 11” are available when each positive component is represented by “0”and each negative component is represented by “1”.

In addition, the symbol configurations of slots in control channelsignal 1 and control channel signal 2 are the same as those in FIG. 5and FIG. 6 respectively. For example, it is assumed that the phase ofthe symbol spread with only the short spreading code SC0 in controlchannel 1 is “00”. And, for example, it is assumed that in controlchannel signal 2, the phase of the symbol spread with only the shortspreading code SCm in Slot 0 is “11”, and the phases of the symbolsspread with only the short spreading code SCm in Slot 2, Slot 4 and Slot6 are “00”.

Mobile station 4 acquires the synchronization of the long spreading codeand the synchronization of the switching timing of reverse and forwardlink according to the initial synchronization method explained in thefirst embodiment. Then mobile station 4 examines a time sequence patternof phases in the I-Q plane of symbols spread with only the shortspreading codes in control channel signal 1 and control channel 2 eachslot. When mobile station 4 detects slots having a pattern in which thephases of control channel signal 1 and control channel signal 2 areprovided according to the order of inverse phase, same phase, same phaseand same phase, mobile station 4 recognizes the head slot of the slotsas first slot, then identifies the head of the slot as a head oftransmission frame.

According to the above manner, it is possible to acquire thesynchronization of the transmission frame, by using the symbol in thecontrol channel spared with the code in which the long spreading codeand the short spreading code are multiplied with no informationtransmitted from a base station on the synchronization of transmissionframe.

In other words, by providing the symbol spread with only the shortspreading code at a part of the control channel signal to transmitcontrol information except for the initial synchronization acquisition,it is possible to acquire the synchronization of the long spreadingcode, the synchronization of the switching timing of reverse and forwardlink and the synchronization of transmission frame, thereby allowingachieving of the initial synchronization method in which the decrease offrequency utilization efficiency due to the initial synchronizationacquisition is suppressed.

As described above, according to the second embodiment, in the CDMA/TDDradio communication system in which the short spreading code and thelong spreading code are multiplied to use, symbols spread with only theshort spreading codes are provided at a certain interval in a unitframe. By detecting the symbols spread with only the short spreadingcodes, it is possible to acquire the synchronization of the longspreading code, the synchronization of the switching of reverse andforward link and the synchronization of the transmission frame. As aresult, in the CDMA/TDD radio communication system, the frequencyutilization efficiency is improved.

Third Embodiment

FIG. 9 is a diagram illustrating a configuration of a phase pattern ofpilot symbols in a control channel to explain an initial synchronizationmethod in the CDMA/TDD communication system according to the thirdembodiment of the present invention. FIG. 9A illustrates patterns of thecase where one frame is divided to 8 slots and Slots 0,2,4 and 6 areassigned to a forward link, FIG. 9B illustrates patterns of the casewhere one frame is divided to 16 slots and Slots 0,2,4,6,8,10,12 and 14are assigned to the forward link, and FIG. 9C illustrates patterns ofthe case where one frame is divided to 16 slots and Slots0,2,4,6,8,10,12,14,18,20,22,24,26,28 and 30 are assigned to the forwardlink.

At this time, mobile station 4 can acquire the synchronization of thelong spreading code and the synchronization of switching timing ofreverse and forward link by the initial synchronization method explainedin the first embodiment. However mobile station 4 has not recognized theslot number yet and has not acquired the synchronization of thetransmission frame.

This embodiment describes about a method to acquire the synchronizationof the transmission frame by using patterns of phases in the I-Q planeof pilot symbols among symbols spread with a code in which a shortspreading code and a long spreading code are multiplied.

It is assumed that the modulation system is QPSK modulation in the samemanner as the second embodiment. As a phase of each symbol in the I-Qplane, 4 types of “00, 01, 10 and 11” are available when each positivecomponent is represented by “0” and each negative component isrepresented by “1”. The symbol configurations of slots in controlchannel signal 1 and control channel signal 2 are the same as those inFIG. 3 and FIG. 4 respectively.

Base stations 1 to 3 transmit pilot symbols in each slot of controlchannel signal 1 according to the patterns illustrated in FIG. 9A.Mobile station 4 acquires the synchronization of the long spreading codeand the synchronization of the switching timing of reverse and forwardlink according to the initial synchronization method explained in thefirst embodiment, then despreads control channel signal 1 with the codein which the long spreading code and the short spreading code aremultiplied.

When the patterns of pilot symbols are the same as those illustrated inFIG. 9A, mobile station 4 compares the phases of the first symbol andthe second symbol with the phases of the third symbol and the fourthsymbol to judge the patterns of pilot symbols. Thus, the slots areidentified as Slot 0, Slot 2, Slot 4 and Slot 6. In other words, it ispossible to acquire the synchronization of transmission frame.

Also in the case of patterns illustrated in FIG. 9B and FIG. 9C, in thesame manner as the case where one frame is divided to 8 slots, mobilestation 4 can acquire the synchronization of transmission frame byjudging the patterns of pilot symbol of each slot to identify the slotnumber.

This embodiment explains about the case where the phase patterns of thefirst symbol and the second symbol of pilot symbols are all “00”.However it is preferable to use any pattern for the first symbol and thesecond symbol when the phase patterns differ each slot. In addition, itis preferable to apply the method of this embodiment with the method toacquire synchronization of transmission frame described in the secondembodiment.

As described above, since the different pattern is provided each slot ofpilot symbols in the symbols spread with the code in which the longspreading code and the short spreading code are multiplied in thecontrol channel, it is possible to acquire the synchronization oftransmission frame by detecting one slot. Further the detection of aplurality of slots allows improving of the reliability of the initialsynchronization acquisition.

As described above, according to the third embodiment, in the CDMA/TDDradio communication system in which the short spreading code and thelong spreading code are multiplied to use, symbols spread with only theshort spreading codes are provided at a certain interval in a unitframe. By detecting the symbols spread with only the short spreadingcodes, it is possible to acquire the synchronization of the longspreading code and the synchronization of the switching of reverse andforward link. Further by detecting symbols spread with the code in whichthe long spreading code and the short spreading code are multiplied, itis possible to achieve the initial synchronization method in which theacquisition of the frame synchronization is performed. As a result, inthe CDMA/TDD radio communication system, the frequency utilizationefficiency is improved.

Fourth Embodiment

The first embodiment to the third embodiment describe about the casewhere, as a short spreading code to spread symbols to be spread withonly a short spreading code in slots in one frame, short spreading codeSC0 that is common in the system is used in control channel signal 1,and short spreading codes SC1 to SC15 are used in control channel signal2. The fourth embodiment of the present invention describes about thecase where a configuration of short spreading codes SC1 to SC15 in aframe is provided according to a predetermined pattern, where shortspreading codes SC0 to SC15 are also used in control channel signal 2 tospread symbols to be spread with only the short spreading code in slotsin the frame.

In the case of detecting the long spreading code timing or the slottiming, in the same manner as the first embodiment to the thirdembodiment, as the first step, the despreading processing is performedto the control channel signal 1 using short spreading code SC0 to detectsymbols with high correlation. The symbols are spread with only theshort spreading code, and suggest candidate symbols for a head of thelong spreading code.

Next, as the second step, the despreading processing is performed to thesymbols with high correlation using short spreading codes SC1 to SC15 todetect the correlation values. These correlation values are stored in amemory. A plurality of candidate symbols for the head of the longspreading code are present in one frame, in this case four candidatesymbols are present in one frame. The four candidate symbols in theframe each is spread with the same or different short spreading code. Inother words, the four candidate symbols in the frame are spread withshort spreading codes that are provided in the frame according to aconfiguration based on the predetermined pattern.

For example, in code pattern #1, the short spreading codes in the frameare all the same SC1. This case of code pattern #1 corresponds to thecases of the first embodiment to the third embodiment. In code pattern#2, the short spreading codes in the frame are SC1 (Slot0), SC2 (Slot2),SC1 (Slot4) and SC2 (Slot6). In code pattern #3, the short spreadingcodes in the frame are SC1 (Slot0), SC2 (Slot2), SC1 (Slot4) and SC3(Slot6). In code pattern #4, the short spreading codes in the frame areSC1 (Slot0), SC2 (Slot2), SC3 (Slot4) and SC1 (Slot6), as shown in FIG.10A.

Accordingly, with respect to the four candidate symbols in the frame,the sum of the correlation values is calculated each code-pattern, andthe code pattern with the maximum sum value is identified as the codepattern for the frame. In other words, in code pattern #1, thecorrelation values obtained by despreading with SC1, SC1, SC1 and SC1are summed. In code pattern #2, the correlation values obtained bydespreading with SC1, SC2, SC1 and SC2 are summed. In code pattern #3,the correlation values obtained by despreading with SC1, SC2, SC1 andSC3 are summed. In code pattern #4, the correlation values obtained bydespreading with SC1, SC2, SC3 and SC1 are summed. The code pattern withthe maximum sum value among thus obtained sum values is identified asthe short code pattern for the frame.

As the code pattern is identified, a value of k (5 to 9) is decidedaccording to the number of the identified code pattern. In this case, atable illustrated in FIG. 10B is used. It is thereby decided that thesymbol spread with only the short spreading code is the kth symbol. Thetiming of switching reverse link and forward link is thus obtained.

Herein, in the cases of code patterns #3 and #4, since the same codesequence is not repeated in the frame, it is possible to acquire thesynchronization of the frame timing according to the above-mentioned twosteps. Accordingly, it is not necessary to perform the below fourthstep.

As the third step, the despreading processing is performed to thecandidate symbols for the head of the long spreading code in the forwardlink using the code in which the long spreading code and the shortspreading code are multiplied so as to detect the head symbol of thelong spreading code in the candidate symbols.

Finally, as the fourth step, the short spreading code is multiplied bythe long spreading code LC at the timing of the long spreading LCaccording to exclusive-OR to obtain the multiplied code, with which thedespreading processing is performed to received signals. Candidates ofthe head of the long spreading code are decode to judge the frametiming.

In the manner described above, the use of the code patter in one framealso enables the apparatus to acquire the synchronization of the longspreading code, the synchronization of switching of reverse and forwardlink, and the synchronization of transmission frame timing, therebyallowing reducing of the synchronization acquisition time.

Fifth Embodiment

FIG. 11 is a block diagram of an initial synchronization section in aradio communication apparatus in the CDMA/TDD radio communication systemaccording to the fifth embodiment of the present invention. In addition,the radio communication apparatus in this embodiment is a mobile station(communication terminal apparatus). And, antennas, radio transmissionand reception sections, modulating and demodulating sections and otherdevices provided in the CDMA radio communication apparatus are the sameas those in an ordinary radio communication apparatus, therefor thoseare not illustrated in FIG. 11.

In FIG. 11, received signal 801 is in dispersing section 809 despreadwith a spreading code generated in spreading code generating section802. Spreading code generating section 802 includes first codegenerating section 803 for generating short spreading codes SC1 to SC15,second code generating section 804 for generating short spreading codeSC0, third code generating section 805 for generating long spreadingcodes LC, and fourth code generating section 806 for generating shortspreading code SC20 to be multiplied by the long spreading code.

Exclusive OR section 807 multiplies a long spreading code of eachcandidate timing by the short spreading code. Switching section 808switches spreading codes generated in the spreading code generatingsection. Despreading section 809 detects the correlation of a receivedsignal with the spreading code. Initial synchronization section 810acquires the initial synchronization using the correlation valueobtained in despreading section 809.

In the configurations described above, it is assumed that base stations1 to 3 transmit control channel signal 1 and control channel signal 2explained in the first embodiment to the third embodiment.

As the first step, initial synchronization section 810 instructsswitching section 808 to output short spreading code SC0 generated insecond code generating section 804 to despreading section 809. Accordingto this instruction, short spreading code SC0 is output to despreadingsection 809.

Despreading section 809 despreads received signal 801 with shortspreading code SC0 by detecting the correlation of each symbol in a slotat each chip timing. The timing, by which the maximum correlation valuein the obtained correlation values is obtained, is the head position ofthe symbol spread with only short spreading code SC0. And, the headposition of a symbol just after the symbol in the slot is a candidate ofthe head position of the long spreading code. It is preferable tointegrate the correlation value at each chip timing for a plurality ofslots to obtain the integration value if necessary, which improves thereliability of detection of the head symbol position.

Next, as the second step, initial synchronization section 810 instructsspreading code generating section 802 to sequentially generate shortcode spreading codes SC1 to SC15 in first code generating 803 at thesame symbol timing as that of the symbol spread with only the aboveshort spreading code SC0. Also initial synchronization section 810instructs switching section 808 to sequentially output short spreadingcodes SC1 to SC15 generated in first code generating section 803 todespreading section 809. According to the instruction, short spreadingcodes SC1 to SC15 are output to despreading section 809 sequentially.

Despreading section 809 detects the correlation of the symbol spreadwith only short spreading code SC0 in received signal 801 with each ofshort spreading codes SC1 to SC15 sequentially. It is preferable tointegrate the correlation of each code a plurality of times to obtainthe integration value if necessary, which improves the reliability ofthe detection of short spreading code SCm. The spreading code with themaximum correlation value among the obtained correlation values isdetected as short spreading code SCm. As explained in the firstembodiment, the symbol spread with only short spreading code SCm is them+4th symbol in the slot, thereby the head position of the slot isdecided. In other words, it is possible to obtain the synchronization ofswitching timing of reverse and forward link. Thereby, it is possible todespread the symbol other than the symbol despread with the short codeonly.

Next, as the third step, initial synchronization section 810 instructsspreading code generating section 802 to sequentially generate longspreading codes LC in third code generating section 805 according to thealready obtained candidate positions for timings of long spreading code.Also initial synchronization section 810 instructs switching section 808to output signals that are generated in exclusive OR section 807 bymultiplying long spreading code LC generated in third code generatingsection 805 by short spreading code SC20 generated in fourth codegenerating section 806 to despreading section 809. According to theinstruction, long spreading code LC and short spreading code SC20 areoutput to despreading section 809.

Despreading section 809 despreads received signal 801 with each code inwhich long code spreading LC of each candidate timing and shortspreading code SC20 are multiplied, and detects the correlationsequentially. It is preferable to obtain the integration value byintegrating the correlation value of the code of each candidate timing aplurality of times to improve the reliability of the candidate timingdetection. The candidate timing, by which the maximum correlation valuein the obtained correlation values is obtained, is detected as thetiming for the long spreading code LC, thus the synchronization of thelong spreading code LC timing is acquired.

Finally, as the fourth step, initial synchronization section 810instructs spreading code generating section 802 to generate longspreading code LC in third code generating section 805 at the timing oflong spreading code LC. Also initial synchronization section 810instructs switching section 808 to output signals that are generated inexclusive OR section 807 by multiplying long spreading code LC generatedin third code generating section 805 by short spreading code SC20generated in fourth code generating section 806 to despreading section809. According to this instruction, the signals in which long spreadingcode LC and short spreading code SC20 are multiplied are output todespreading section 809 via switching section 808.

Despreading section 809 despreads received signal 801 with the code inwhich long spreading code LC and short spreading code SC20 aremultiplied, and detects the correlation. Despreading section 809 obtainsphases in the I-Q plane using the detected correlation values, andjudges the phase patterns of pilot symbols.

It is preferable to judge phases of pilot symbols of a plurality offrames to improve the judgement reliability. The slot number is decidedwhen the pilot symbol pattern is conformed (to the known pattern),thereby making it possible to acquire the synchronization oftransmission frame timing.

It is thus possible to despread both of symbols spread with the code inwhich long spreading code LC and short spreading code SC20 aremultiplied and symbols spread with only short spreading code SC20.

As described above, according to the fifth embodiment, in the CDMA/TDDradio communication system, a mobile station apparatus comprises aprocessing section for despreading with the code in which the longspreading code and the short spreading code are multiplied, and anotherprocessing section for despreading with short spreading code. Then themobile station apparatus acquires the initial synchronization using theinitial synchronization method according to either of the firstembodiment to the fifth embodiment. The mobile station apparatus thusreduces the initial synchronization acquisition time, thereby resultingin the radio communication system with high frequency utilizationefficiency.

Sixth Embodiment

FIG. 12 is a block diagram illustrating a primary configuration of aradio communication apparatus in the CDMA/TDD according to the sixthembodiment of the present invention. In addition, it is assumed that theradio communication apparatus in this embodiment is a base station. And,antennas, radio transmission and reception sections, modulating anddemodulating sections and other devices provided in the CDMA radiocommunication apparatus are the same as those in an ordinary radiocommunication apparatus, therefor those are not illustrated in FIG. 12.

In FIG. 12, first code generating section 901 generates long spreadingcode LC. Second code generating section 902 generates short spreadingcode SC20. Third code generating section 903 generates short spreadingcode SC0. Fourth code generating section 904 generates short spreadingcode SC5. Fifth code generating section 905 generates short spreadingcode SC21. Sixth code generating section 906 generates short spreadingcode SC22.

Exclusive OR section 907 multiplies long spreading code LC by shortspreading code SC20. Exclusive OR section 908 multiplies long spreadingcode LC by short spreading code SC21. Exclusive OR section 909multiplies long spreading code LC by short spreading code SC22.

Switching section 910 switches a spreading code of control channel 1.First spreading section 911 and third spreading section 913 spreadcontrol channel signal 1. Second spreading section 912 and fourthspreading section 914 spread control channel signal 2. Multiplexingsection 915 synthesizes spread signals.

In the configuration described above, first code generating section 901generates long spreading code LC, second code generating section 902generates short spreading code 20 to be multiplied by long spreadingcode LC in exclusive OR section 907. The multiplied code is input toswitching section 910.

Third code generating section 903 generates short spreading code SC0 forthe symbol to be spread with only the short spreading code. Switchingsection 910 switches, according to the slot configuration example inFIG. 7, the code in which long spreading code LC and short spreadingcode SC20 are multiplied to output to first spreading section 911.

Control information 1′ including the pilot symbol indicative of a pilotsymbol pattern shown in FIG. 9A is input to first spreading section 911.First spreading section 911 spreads control information 1′ with theswitched spreading code to input to multiplexing section 915.

Fourth code generating section 904 generates short spreading code SC5according to the slot configuration in FIG. 8 to input second spreadingsection 912. In this example, since the object symbol is the ninthsymbol, fourth code generating section 904 generates short spreadingcode SC5. Generally, fourth code generating section 904 generates shortspreading code SCk-4 when the object symbol is the kth symbol. Secondspreading section 912 spreads control information 2′ with shortspreading code SC5 to input to multiplexing section 915.

Fifth code generating section 905 generates short spreading code SC21.Exclusive OR section 908 multiplies short spreading code SC21 by longspreading code LC to input to third spreading section 913. Thirdspreading section 913 spreads communication information 1′ with the codein which short spreading code SC21 and long spreading code LC aremultiplied to input to multiplexing section 915.

Sixth code generating section 906 generates short spreading code SC22.Exclusive OR section 909 multiplies short spreading code SC22 by longspreading code LC to input to fourth spreading section 914. Fourthspreading section 914 spreads communication information 2′ with the codein which short spreading code SC22 and long spreading code LC aremultiplied to input to multiplexing section 915.

Multiplexing section 915 multiplexes control channel 1, control channel2, communication channel 1 and communication channel 2 to generatetransmission signals. The signal sequence illustrated in FIG. 3 is thusgenerated.

The above processing makes it possible to reduce the acquisition time ofthe synchronization of the long spreading code, the synchronization ofswitching timing of reverse and forward link and the synchronizationtransmission frame, thereby making it possible to suppress the decreaseof frequency utilization efficiency due to the initial synchronizationacquisition.

As described above, the sixth embodiment provides the base stationapparatus in the CDMA/TDD radio communication system comprising theprocessing section for transmitting symbols spread with the code inwhich the long spreading code and the short spreading code aremultiplied, and the symbol spread with only the short spreading code ina certain interval, based on the initial synchronization methodaccording to either of the first embodiment to the fourth embodiment,which allows the system to have the reduced acquisition time in theinitial synchronization and improved frequency utilization efficiency.

Seventh Embodiment

A CDMA/TDD radio communication system according to the seventhembodiment of the present invention is composed of a radio communicationapparatus such as the base station illustrated in FIG. 12 that isexplained in the sixth embodiment and a radio communication apparatussuch as the mobile station illustrated in FIG. 11 that is explained inthe fifth embodiment.

In other words, the radio communication system of the seventh embodimentperforms the acquisitions of synchronization of the long spreading code,the synchronization of switching timing of reverse and forward link, andthe synchronization of transmission frame.

The above processing makes it possible to reduce the acquisition time ofthe synchronization of the long spreading code, the synchronization ofswitching timing of reverse and forward link and the synchronization oftransmission frame, thereby suppressing the decrease of frequencyutilization efficiency due to the initial synchronization acquisition.

As described above, it is possible by the seventh embodiment to achievethe radio communication system comprising the CDMA/TDD radiocommunication apparatus including the processing section fortransmitting symbols spread with the code in which the long spreadingcode and the short spreading code are multiplied, and the symbol spreadwith only the short spreading code in a certain interval, based on theinitial synchronization method according to either of the firstembodiment to the fourth embodiment, and comprising the CDMA/TDD radiocommunication apparatus including the processing section for despreadingusing the code in which the long spreading code and the short spreadingcode are multiplied, and the another processing section for despreadingusing the short spreading code, to perform the initial synchronizationacquisition using the initial synchronization method according to eitherof the firs embodiment to the fourth embodiment. It is thereby possibleto reduce the acquisition time in the initial synchronization andimprove the frequency utilization efficiency.

It is apparent as described above to acquire the synchronization of thelong spreading code, the synchronization of reverse and forward linkswitching, and the synchronization of transmission frames by providingthe symbols spread with only the short spreading codes and detecting thesymbols spread with only the short spreading codes in the CDMA/TDD radiocommunication system in which the short spreading code and the longspreading code are multiplied to use. It is thereby possible to reducethe acquisition time in the initial synchronization and improve thefrequency utilization efficiency.

This application is based on the Japanese Patent Application No.HEI9-345820 filed on Dec. 1, 1997, entire content of which is expresslyincorporated by reference herein.

1. A base station apparatus in a CDMA/TDD mobile communication system inwhich a signal is formed employing a frame configuration with aplurality of time slots, the base station apparatus comprising: a firstcontrol channel former that forms a first control channel including afirst symbol that is spread with a first short spreading code used toacquire synchronization at a mobile station; a selector that selects asecond short spreading code, out of a plurality of short spreadingcodes, and a phase difference between the first short spreading code andthe second short spreading code, based on a size of an offset and anorder of time slots in the plurality of time slots, the size beingdetermined for a cell; a second control channel former that forms asecond control channel including a second symbol spread with a secondshort spreading; a traffic channel former that forms a traffic channelincluding a symbol spread with a long spreading code used to identifythe cell; and a transmitter that transmits the first symbol in the firstcontrol channel and the second symbol in the second control channel, ata same timing as the offset after a division of a time slot, theselected phase difference being provided between the first symbol andthe second symbol, and transmits the symbol spread with the longspreading code in the traffic channel.
 2. The apparatus of claim 1,wherein the short spreading code is selected based on a candidate longspreading code.
 3. The apparatus of claim 1, wherein the second shortspreading code is selected according to a number that represents one ofthe plurality of short spreading codes, the number being determinedbased on the size of the offset and the order of time slots in theplurality of time slots.
 4. The apparatus of claim 1, wherein the secondshort spreading code is selected according to a periodic sequentialordering of codes over the plurality of time slots, the periodicordering being determined based on the size of the offset and the orderof time slots in the plurality of time slots.
 5. The apparatus of claim1, wherein the phase difference is selected according to a periodicsequential ordering of the phase difference between the first shortspreading code and the second short spreading code over the plurality oftime slots, the periodic ordering being determined based on the size ofthe offset and the order of time slots in the plurality of time slots.6. The apparatus of claim 1, wherein the second short spreading code andthe phase difference are selected according to a periodic sequentialordering of a combination of a number that represents a short spreadingcode and a phase difference between the first short spreading code andthe second short spreading code over the plurality of time slots, theperiodic ordering being determined based on the size of the offset andthe order of time slots in the plurality of time slots.
 7. A mobilestation apparatus in a CDMA/TDD mobile communication system in which asignal is received employing a frame configuration with a plurality oftime slots, the mobile station apparatus comprising: a first codegenerating section operable to generate a first short spreading code; asecond code generating section operable to generate a second shortspreading code; a dispreading section operable to: (i) despread areceived signal with a first short spreading code, obtain a firstcorrelation value and a first correlation phase, and acquire a firstperiodic timing, and (ii) despread the received signal with a pluralityof second short spreading codes at the periodic timing, and obtain asecond correlation value and a second correlation phase; and an initialsynchronization section operable to detect a size of an offsetdetermined for a cell, the offset covering from a division of a timeslot to the first periodic timing, and an order of time slots in aplurality of time slots, based on the second correlation and a phasedifference between the first correlation and the second correlation, andacquires a second periodic timing which precedes the first periodictiming by the detected offset, wherein the dispreading section is alsooperable to despread the received signal with a long spreading code foridentifying the cell, based on the second periodic timing and the orderof time slots in the plurality of time slots.
 8. The apparatus of claim7, wherein the initial synchronization section is operable to detect acandidate long spreading code based on the second correlation and thephase difference between the first correlation and the secondcorrelation.
 9. The apparatus of claim 7, wherein the initialsynchronization section is operable to detect the size of the offsetbased on a number that represents a code detected in the secondcorrelation detector.
 10. The apparatus of claim 7, wherein the initialsynchronization section detects the size of the offset using a periodicsequential ordering of the second correlation detection value over theplurality of time slots.
 11. The apparatus of claim 7, wherein theinitial synchronization section detects the size of the offset using aperiodic sequential ordering of a phase difference between the firstcorrelation phase and the second correlation phase over the plurality oftime slots.
 12. The apparatus of claim 7, wherein the initialsynchronization section detects the size of the offset using a periodicsequential ordering of a combination of a number that represents a codedetected in the second correlation detector and a phase differencebetween the first correlation phase and the second correlation phase.13. A transmission method in a CDMA/TDD mobile communication system inwhich a signal is formed employing a frame configuration with aplurality of time slots, the method comprising: forming, in a firstcontrol channel former, a first control channel including a first symbolthat is spread with a first short spreading code used to acquiresynchronization at a mobile station; selecting, in a selector, a secondshort spreading code among a plurality of short spreading codes and aphase difference between the first short spreading code and the secondshort spreading code, based on a size of an offset and an order of timeslots in a plurality of time slots, the size being determined for acell; forming, in a second control channel former, a second controlchannel including a second symbol spread with the second short spreadingcode; forming, in a traffic channel former, a traffic channel includinga symbol spread with a long spreading code used to identify the cell;and transmitting, in a transmitting section, the first symbol in thefirst control channel and the second symbol in the second controlchannel at a same timing as the offset after a division of a time slot,the selected phase difference being provided between the first symboland the second symbol, and transmitting the symbol spread with the longspreading code in the traffic channel.
 14. The method of claim 13,wherein the second short spreading code is selected based on a candidatelong spreading code.
 15. The method of claim 13, wherein the a secondshort spreading code is selected according to a periodic sequentialordering of codes over a plurality of time slots, the periodic orderingbeing determined based on the size of the offset and the order of timeslots in the plurality of time slots.
 16. The method of claim 13,wherein the phase difference is selected according to a periodicsequential ordering of a phase difference between the first shortspreading code and the second short spreading code over a plurality oftime slots, the periodic ordering being determined based on the size ofthe offset and the order of time slots in the plurality of time slots.17. The method of claim 13, wherein the second short spreading code andthe phase difference between the first short spreading code and thesecond short spreading code are selected according to a periodicsequential ordering of a combination of a number that represents a shortspreading code and the phase difference between the first shortspreading code and the second short spreading code over the plurality oftime slots, the periodic ordering being determined based on the size ofthe offset and the order of time slots in the plurality of time slots.18. A receiving method in a CDMA/TDD mobile communication system thatreceives a signal employing a frame configuration with a plurality oftime slots, the received signal being spread by a long spreading code,the method comprising: despreading, in a despreading section, a receivedsignal using a first short spreading code, obtaining a first correlationvalue and a first correlation phase, and acquiring a first periodictiming; despreading, in the dispreading section, the received signalusing a plurality of kinds of second short spreading codes at the firstperiodic timing, and obtaining a second correlation value and a secondcorrelation phase; obtaining, in an initial synchronization section, asize of an offset determined for a cell, the offset covering from adivision of a time slot to the first periodic timing, and an order oftime slots in a plurality of time slots, based on the second correlationvalue and a phase difference between the first correlation phase and thesecond correlation phase, and acquires a second periodic timing whichprecedes the first periodic timing by the detected offset; anddespreading, in the dispreading section, the received signal using along spreading code for identifying the cell, based on the secondperiodic timing and the order of time slots in the plurality of timeslots.
 19. The method of claim 18, wherein a candidate long spreadingcode is obtained using the second correlation value and the phasedifference between the first correlation phase and the secondcorrelation phase.
 20. The method of claim 18, wherein the size of theoffset is obtained using a periodic sequential ordering of correlationvalue over the plurality of time slots.
 21. The method of claim 18,wherein the size of the offset is obtained using a periodic sequentialordering of the phase difference between the first correlation phase andthe second correlation phase over the plurality of time slots.
 22. Themethod of claim 18, wherein the size of the offset is obtained usingperiodic sequential ordering of a combination of a number thatrepresents a code of the plurality of kinds of second short spreadingcodes and the phase difference between the first correlation phase andthe second correlation phase.